This grant evaluates how gamma irradiation affects the biomechanics of frozen goat bone-patellar tendon-bone allografts (PTBs) used to replace the anterior cruciate ligament (ACL). With growing concern that sterilly- procured allografts could transmit infectious diseases such as AIDS, tissue sterilization methods such as gamma irradiation have recently been advocated. Preliminary studies in our laboratory indicate that 2 Mrads of gamma irradiation does not significantly reduce the initial or inherent material properties of frozen goat PTB specimens. However, no study has determined whether this level of irradiations alter graft biomechanics after implantation. Two studies will be preformed to examine this question. Study 1 will be devoted to finding a single set of reproducible initial conditions for installing a PTB. Our goal is to restore the in vitro anterior-posterior translations of the intact knee. To do this we will develop methods to control the graft tension and flexion angle at surgery as well as the attachment site location and bone tunnel orientations of the graft ends. We do not seek the optimum set of conditions but only one reproducible set. Study 2 is designed to test the hypothesis that 6 months after surgery, there are no significant differences in structural mechanical or material properties between frozen and 2 Mrad irradiated frozen allografts. Paired grafts from donor animals will be either frozen or frozen and irradiated. The pair will be installed using phased surgeries. The design will block for time-order effects, potential right vs left and animal-to-animal variabilities. Power analyses will ensure adequate sample size to detect statistical differences due to the treatment variable if they exist. Tissues will be mechanically evaluated at six months after when bone healing is completed and the rate of return in mechanical properties has slowed. The results will indicate whether a commonly used irradiation method is detrimental to the mechanical integrity of an anterior cruciate ligament replacement. The study will also be the basis for examining biological changes associated with this treatment method.